In the literal sense of the word
The problem for many of them was that English had not been compulsory at school beyond S2. Some claimed that the subject had been taught using dingy resources in dingy classrooms by dingy middle-aged men and that they couldn't get shot of it quickly enough. A few even seemed to wear their lack of ability with pride.
Though it seemed to vary from local authority to local authority, many claimed they would like to be good at literacy teaching but the barrier seemed to be training. Despite the subject being compulsory at all stages in primary schools for more than a decade, they did not think there had been a satisfactory provision to address their self-confessed shortcomings.
When McCrone came in, it became common for one teacher to be the literacy specialist in a school. Droves of primary teachers who were not confident in teaching literacy then grasped the opportunity to enhance their skills by sitting in with the specialist during their non-teaching time. They knew that they might not always have the services of a local expert and felt the need to get themselves up to speed. Enlightened management, aware that this time could have been used for marking or preparation, set some of it off against the 35 hours' CPD allocation.
Of course, all of this is havers. Never once did a teacher confess to being illiterate. Even if they felt they were, I doubt anybody would be willing to admit it. Change "English" or "literacy" to "science" and "illiterate" to "non-scientific" and you have something approaching the truth.
Where I fear it all falls apart is in the bit about the use of McCrone time. Is there a missed opportunity here, or is the problem yet again one of workload? I can't answer that. I'd like to think I'm literate and scientific, but I'm not omnipresent.
Gregor Steele found that most primary teachers were less illiterate than they thought they were.